Dielectric relaxation modes in cholesteryl oleyl carbonate observed by non-linear dielectric spectroscopy

摘要

The non-linear dielectric spectra of chiral crystal cholesteryl oleyl carbonate (COC) were recorded in the frequency range of 1–100 MHz in the presence of strong static electric field E_0 = 1 × 10~7 V/m. The measurements were performed in the cholesteric nematic phase N~*. The results revealed two regions in the temperature dependence of the chemical relaxation time behaviour, corresponding to two-phase coexistence region (blue phase + N~*) and homogenous cholesteric phase N~*, respectively. In the non-linear dielectric relaxation spectra, three absorption bands, related to the different molecular rotations of individual molecules around axes and director, have been observed. The negative components of the frequency dependence of the non-linear dielectric phenomena concern the Langevin saturation of the dipoles orientation in strong electric field.